Production of alicyclic ketones from alicyclic alcohols



Patented Jan. 4, 1944' I PRODUCTION OF ALICYCLIC KETONES FROM ALICYCLICALCOHOLS Friedrich Laucht, Leuna, Germany; vested in the Alien PropertyCustodian No Drawing. Application December 6,1040, Serial No. 368,858.In Germany December 13,

1 939 7 Claims.

The present invention relates to the production of alicyclic ketonesfrom alicyclic alcohols.

The preparation of ketones by the catalytic dehydrogenation of secondaryalcohols has heretofore been suggested. Thus, vaporized secondaryalcohols have been led over copper-zinc alloys,

in particular over alloys containing equal amounts of copper and zinc.

In the production 01' alicyclic'ketones with the aid of such catalysts,there i usually observed a too far-reaching dehydrogenation with theformation of phenol and, furthermore, a dehydration with the formationof olefinic bodies. .It is very difficult to free alicyclic ketones fromphenols. The distillation in the presence of alkali metal hydroxides,which would keep back the phenols, cannot be carried out, because theketones undergo intermolecular condensations'in the presence of alkalimetal hydroxides. It is also very difficult to wash out the phenols withdilute alkali metal hydroxide solutions because of the high density ofalicyclic ketones. Cyclohexanon may be, it is true, separated fromphenol by rectification. This process, however, involves additionalexpenses; it cannot be used at all when purifying mixtures ofcyclohexanone and its homologues because of the overlapping of theboiling points of the ketones with those of the phenols.

It is an object of the present invention to produce alicyclic ketoneswhich are free from phenolic bodies and free from substantial amounts'of olefines by carrying out the dehydrogenation at temperatures notsubstantially exceeding 500 0. with the aid of zinc alone or of zinccontain ing up to 20 per cent of copper, preferably not more than percent or copper. According to the present invention there may be used ascatalyst zinc alone or zinc being admixed or alloyed with small amountsof copper amounting up to per cent. Small amounts of other ingredientsusually to be found in the commercial grades of zinc do not prevent thesatisfactory operationof the process.

The invention may be used in the dehydrogeneration of monocyclicalicyclic alcohols, such as cyclohexanol and its homologues and mixturesthereof, as they are obtained in the hydrogenation of monocyclicphenols, as well as in that of other alicyclic alcohols, e. g. ofdecahydronaphthoL The catalysts are used in such a form as to oiier alarge surface to the gaseous alcohol, While care is taken that the flowof the gases is not hindered. Preferably, the catalysts are used in theform of netting, rolled-up netting, spirals, threads or cuttings.

The vaporized alcohols may [be led over'the catalyst together with inertdiluent gases, as for example with nitrogen, hydrogen orsteam. It ispreferable to work at normal pressure; however, the process may also becarriedout under subatmospheric or superatmospheric pressure.

The most favorable reaction temperature de- I pends on the catalyst.Generally speaking, the most favorable reaction temperature may beincreased within the rangeof fromabout 380 to 500 C. with'increasingcopper content. While temperatures from about 380 to 390 C. are most.favorable in the use of zinc alone, the optimal temperature amounts toabout 420 C. for a cop per content of 5 per cent, to about 440 C. for acopper content of 10 per cent, and to from about 460 to 480 C. for acopper content of 15 per cent. Other temperatures within the range offrom 380 to 500 C. may be used for the various catalysts set forth abovewithout the formation of undesirable by-products, the rate of conversionbeing somewhat poorer.

Furthermore, it is preferable to avoid temperatures above the meltingpoint of the catalysts because otherwise the surface ofiered to thealcohol vapors becomes small. When working below 380 C., the rate ofconversion decreases, in other words mixtures of alcohols and ketonesare obtained which are useful for many technical purposes. Working below300 C. is no longer eco- 7/ nomical due to the very slow speed ofconversion.

The following examples will serve to illustrate the nature of thisinvention. It is, however, not

restricted to these examples.

Example 1 1 kilogram of vaporized cyclohexanol per hour is led at 440 C.through a tube made from V2A steel of 2 meters length and 36 millimetersinternal diameter which is charged with 1.5 kilograms of turnings of analmy consisting of per cent of zinc and 10 per ceiitof copper. Thevapors emerging from the tube arewondensed. The condensate contains from90 to per cent of cyclohexanone, less than 1 per cent of cyclohexene,the balance consisting of unchanged cyclohexanol.

Example 2 i 15 grams of vaporized methylcyclohexanol (obtained byhydrogenation of a mixture of isomeric' cresols) per hour are led at 420C. through a glass tube of 80 centimeters length and 20 millimetersinternal diameter charged with 40 grams of turnings of an alloycontaining 95 per cent of zinc and 5 per cent of copper. By condensingthe vapors emerging from the tube a liquid is obtained consisting offrom 85 to 90 per cent of methylcyclohexanone, unchangedmethylcyclohexanol and less than 1 per cent of methylcyclohexene.

Example 3 1 kilogram of a mixture of 40 per cent of cyclohexanol, 40 percent of methylcyclohexanol and 20 per cent of dimethylcyclohexanol(obtained by hydrogenating a mixture of phenol, cresols and xylenols) isled per hour at about 390 C. through a tube as described in Example 1which is charged with 1 kilogram of zinc turnings. By condensing thevapors emerging from the tube. a mixture is obtained which contains-from 85 to 90 per cent of alicyclic ketones, unchanged alicyclicalcohols and less than 1 per cent of cyclic olefines.

What I claim is 1. A process for the production of alicyclic ketones bycatalytic dehydrogenation of alicyclic alcohols which consists inleading vaporized alicyclic alcohols cimtaining at least 6 carbon atomsat temperatures between 300 and 500 C. over a metallic body selectedfrom the group consisting of zinc and zinc containing up to 20 per centof copper.

2. A process for the production of alicyclic ketones by catalyticdehydrogenation of alicyclic alcohols which consists in leadingvaporized alicyclic alcohols containing at least 6 carbon atoms attemperatures between 380 and 500 C. over a metallic body selected fromthe group consisting of zinc and zinc containing up to 20 per cent ofcopper.

3. A process for the production of alicyclic' ketones by catalyticdehydrogenation of alicyclic alcohols which consists in leadingvaporized monocyclic alicyclic alcohols containing at least 6 carbonatoms at temperatures between 380 and 500 C. over a metallic bodyselected from the group consisting of zinc and zinc containing up to 20per cent of copper.

4. A process for the production of alicyclic ketones by catalyticdehydrogenation of alicyclic alcohols which consists in leadingvaporized alicyclic alcohols containing at least 6 carbon atoms attemperatures between 300 and 500 C. over zinc containing up to 15 percent of copper.

5. A process for the production of alicyclic ketones by catalyticdehydrogenation of alicyclic alcohols which consists in leadingvaporized cyclohexanol at temperatures between 380 and 500 C. over zinccontaining up to 15 per cent of copper.

6. A process for the production of alicyclic ketones by catalyticdehydrogenation of alicyclic alcohols which consists in leadingvaporized methylcyclohexanol at temperatures between 380 and 500 C. overzinc containing up to 15 per cent of copper.

7. A process for the production of alicyclic ketones by catalyticdehydrogenation of alicyclic alcohols which consists in leadingvaporized dimethylcyclohexanol at temperatures between 380 and 500Clover zinc containing up to 15 per cent of copper.

FRIEDRICH LAUCHT.

